Photochromism is a phenomenon that is drawing attention in these several years, and is a reversible action of a compound which quickly changes its color when it is irradiated with light containing ultraviolet rays such as sunlight or light of a fluorescent lamp and resumes its initial color when it is no longer irradiated with light but is placed in a dark place. The compound having this property is called photochromic compound. Various compounds have so far been synthesized but no particular common nature is recognized in their structures.
The present inventors have forwarded the study concerning a series of photochromic compounds, have succeeded in synthesizing novel photochromic compounds such as fulgimide compounds, spirooxazine compounds and chromene compounds, have discovered that these compounds exhibit excellent photochromic properties, and have already proposed these compounds.
Through the study conducted by the present inventors up to now, it has been learned that the photochromic properties such as color density and fading rate of the photochromic compound are exhibited considerably sluggishly in the polymer as compared in a solution. This phenomenon becomes conspicuous particularly in a compound having photochromic molecules of large sizes. The development of this phenomenon is attributed to that free space in which the photochromic compound molecules are allowed to freely move is very limited in a matrix of polymer compared to that of in a solution.
In order to solve the above-mentioned problem, it can be contrived to make the base member soft by lowering the glass transition temperature of polymer of the matrix or to broaden free space in the matrix.
However, when a matrix having a low glass transition temperature is simply used, hardness is lost bringing about a problem when the composition is used for the applications where a hardness is required, such as lenses. Further, when polymer having large free space is used as a matrix, the hardness of the polymer is usually much dependent upon the temperature. Even those that exhibit a relatively high hardness near room temperature show a rapidly dropped hardness at high temperatures (hereinafter also referred to as having a low heat resistance) and further show a decreased impact resistance.
U.S. Pat. No. 5,395,566 teaches that the use of a polymerizable monomer having an epoxy group in combination with a photochromic compound, helps improve light resistance for the photochromic properties. The above technology, however, does not at all teach the use of a polyfunctional monomer in combination with a difunctional monomer which, when homopolymerized, exhibits an L-scale Rockwell hardness of not smaller than 60, in addition to using the above polymerizable monomer having an epoxy group. Therefore, the cured product that is obtained has a low hardness and poor impact resistance.
The specification of U.S. Pat. No. 5,739,243 teaches a system of a combination of a particular long-chain alkylene glycol dimethacrylate and a polyfunctional methacrylate having three or more radically polymerizable groups. From this combination is obtained a cured product having improved color density and fading rate. However, this technology is for obtaining a matrix excellent in flexibility. With this combination as shown in working examples, the matrix has such problems as a decreased hardness, a decreased heat resistance and much optical distortion.
Further, the specification of U.S. Pat. No. 5,811,503 discloses a system of a combination of a long-chain alkylene glycol dimethacrylate, a dimethacrylate, and a polyfunctional methacrylate having three or more radically polymerizable groups. Though improved color-developing rate and fading rate are exhibited, this combination, too, has such defects that the matrix exhibits a decreased hardness, a decreased heat resistance and much optical distortion.
The specification of PCT International Patent Application 97/03373 discloses a combination of a dimethacrylate with bisphenol A as a skeleton, a monofunctional styrene and a long-chain alkyl monofunctional methacrylate. However, this combination, too, has such defects that the matrix exhibits decreased hardness, a decreased heat resistance and much optical distortion.
The specification of U.S. Pat. No. 5,708,064 teaches the use of a particular polymerizable monomer for imparting a large refractive index to a polymer in combination with a particular polymerizable monomer rich in flexibility. In this technology, however, examples of the polymerizable monomer for imparting a large refractive index are monofunctional monomers or those, which when homopolymerized, exhibit an L-scale Rockwell hardness of smaller than 60, such as bisphenol A bismethacrylate, phenoxyethylmethacrylate, styrene, and α-methyl styrene, from which cured products having a high hardness cannot be obtained. Concerning the particular system of the above combination, the above technology does not, either, disclose the use of a polyfunctional polymerizable monomer that satisfies the requirement of L-scale Rockwell hardness of not smaller than 60 degrees. Thus, this technology, too, teaches a cured product having a low hardness, an inferior heat resistance and an inferior impact resistance.
As described above, no compound is ever satisfying both photochromic properties and matrix properties.